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## Inner Solar System Viewer

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Six bodies are depicted here. The Sun (yellow) is at the center of the
diagram, and the terrestrial planets Mercury (grey), Venus (green),
Earth (blue), and Mars (red) follow nearly circular orbits around the
Sun. You can change the orbit of
the sixth object, an asteroid (red, connected to Sun by yellow line),
with the sliders underneath the diagram.

The ** Semimajor Axis, a, ** is measured in units of
Astronomical Units (AU). One AU is the distance from the Earth to the
Sun.
The orbial ** Eccentricity, e,** is unitless. This
parameter is a measure of the roundness of the orbit and can take on
any positive value.
- For e = 0, the orbit is a circle
- For 0 < e < 1, the orbit is an ellipse.
- For e > 1, the orbit is a hyperbola.

The ** Longitude of pericenter, w (omega),** is an
angle with units of degrees. Omega is measured from a reference
direction, here the positive x-axis (green line at 3 o'clock), to
pericenter (the closest approach of the orbit to the Sun).

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Created on Nov 21, 1998.